WinXP guest does not boot after upgrade to 1.6.0

Description

I have been running VirtualBox 1.5.6 on an Ubuntu Gutsy host. I have installed a WinXP guest some month ago.

After upgrading VirtualBox from 1.5.6-28266 to 1.6.0-30421 this WinXP guest does not boot any more. It stops just after the Bios screen with 'Media error'. I did not touch the configuration of this guest.

This might be caused by a different hard disk layout presented by the bios:

Booting the guest system from a knoppix cd both VirtualBox versions show a disk geometry of CHS=21845/16/63 according to fdisk -l. In both VirtualBox versions I can access /dev/hda1 as a valid windows partition.